perf(session-parser): read each session file once in extractCostlyPrompts

[danikdanik]

Why

extractCostlyPrompts() read the same session .jsonl file from disk twice on every call: once inside parseSessionTurns() (which it calls for per-turn cost data) and once more directly, to walk the file for user-message text. Session transcripts can be multiple megabytes, and the audit / dashboard path calls extractCostlyPrompts() once per costly session, so each call paid for two full readFileSync + two split("\n") passes over the same bytes.

What

extractCostlyPrompts() now reads and splits the file once and reuses the resulting lines for both the per-turn parse and the user-text walk. Net effect per call: one statSync + one readFileSync + one split instead of two of each. As a side benefit, pairing user text to turns is now immune to the file changing between the two former reads (a small time-of-check window is gone).

How

• Extracted a private parseSessionTurnsFromLines(lines, openclawDir) core holding the existing turn-parsing logic verbatim.
• parseSessionTurns(filePath, ...) now reads + splits, then delegates to that core. Its public signature and behavior are unchanged.
• extractCostlyPrompts() reads + splits once, calls the core for turns, then walks the same lines array for user text. Because both walks operate on the identical lines, the turn-index pairing stays exactly aligned (the constraint already flagged by the in-code comment).

Validation

• npm run build (tsc) passes; compiled dist/ regenerated and committed in lockstep with src (repo convention).
• Behavior verified byte-identical before/after on a fixture exercising normal turns, a sidechain message, a tool_result-only user message, and a trailing user message (the turn-index-alignment-sensitive cases).
• Public API surface unchanged: no .d.ts signature change; the new helper is private.

Scope

Deliberately narrow. Left for a possible follow-up: the broader audit pipeline still reads each file independently via parseSession, extractCostlyPrompts, and loadMessagesFromSessionFile; and the statSync / read / 50MB-guard block is duplicated across the two functions.

[alexgreensh]

Merged in v5.11.13 — single read plus the turn-pairing-stability bonus. Thanks, Dani.